Have you ever wondered how scientists measure the distance between us and stars thousands of light years away? A pretty cool video created by the Royal Observatory in Greenwich, as part of their micro exhibition “Measuring the Universe: From the transit of Venus to the edge of the cosmos”, explains in simple fashion just how this is achieved.

It all boils down to three simple aspects of physics: parallax, standard candles, and the Doppler Effect. Parallax is the method of measuring an objects distance from yourself by measuring its relative movement when compared to another object even further in the distance. If you know a light sources luminosity then you can work out it’s distance given how bright it actually appears, stars with a known luminosity are standard candles. The Doppler Effect is the name given to the change in frequency of a wave to an observer moving relative to its source. This can be applied to the light waves emitted by an object as it is traveling, an object moving towards you will have the waves it’s emitting blue shifted and those moving away will be red shifted, due to the change in frequency. Because the universe is expanding, all distant galaxies are red shifted and we can measure their distance based on the amount of red shift.

What’s really interesting is how all three link together. Parallax is limited to only measuring the distance to nearby stars and obviously we can only measure the distance of standard candles due to their very nature of needing a known luminosity, but we can build all three together. By knowing the distance from Earth to the Sun we can measure the distance of nearby stars using parallax, if these are standard candles then, by comparing, them we can measure the distance to further stars and galaxies. By studying the motions of these galaxies with standard candles we use red shift to measure distances throughout the universe.